Gaseous discharge display device with a layer of electrically resistant material

ABSTRACT

A visual display device incorporates an array of direct-current devices. A plurality of gas-filled cavities, each forming a discharge space for one discharge device, or a single gas-filled cavity common to all discharge devices is formed between a first and a second block of electrically insulating material. A plurality of transparent anode conductors on a face of a first block of electrically insulating material, sealed to the first block, and in registration with the cavities, form anode electrodes for one co-ordinate of the array. Cathode electrodes are carried by a face of the second block of electrically insulating material, and those cathode electrodes of the other co-ordinate of the array are connected by way of electrically resistive material to one of a plurality of cathode conductors. The cathode conductors, which are isolated from the discharge space or spaces, cathode electrodes and electrically resistive material are all carried on said face of the second block. The first and second blocks may be spaced through a spacer around the edge of the display device or by a third block defining the discharge spaces. A layer of insulating material covers the face of the block, the resistive material and the cathode conductors, except in the vicinity of the cathode electrodes.

United States Patent [191 Walters GASEOUS DISCHARGE DISPLAY DEVICE WITH A LAYER OF ELECTRICALLY RESISTANT MATERIAL [76] Inventor: Frank Walters, Bury, England Notice: The portion'of the term of this 1 patent subsequent to May 22, 1990,

has been disclaimed.

[22] Filed: Oct. 3, 1972 [21] Appl. No.: 294,560

Related US. Application Data [63] Continuation-impart of Ser. No. 144,872, May 19,

l97l, Pat. No. 3,735,183.

[30] 7 Foreign Application Priority Data M5 0. 1970 {Great Britain 24359/70 May 30, 1970 Great Britain 26198/71 521' US. Cl. 313/188, 313/217, 313/220,

, v y 313/221,315/58,3l5/169TV [51] Int. Cl I-I0lj 17/34, I-lOij 61/04 [58] Field of Search 313/188, 217, 220, 221;

l 315/52, 58, 59, 169 R, 169 Tv [56] References Cited UNITED STATES PATENTS 3,206,638 9/1965 ,Moore; 315/169 TV X 3,334,269 8/1967 L'l-leureux 315/169 rv x 3,553,458 lll97l Schagen....- 315/169 R X 3,603,837 9/1911 Turner 313/220 1*Mar. 19, 1974 Primary Examiner-Palmer C. Demeo Attorney, Agent, or Firm-Cameron, Kerkam, Sutton, Stowell & Stowell 57 ABSTRACT A visual display device incorporates an array of directcurrent devices. A plurality of gas-filled cavities, each forming a discharge space for one discharge device, or

g a single gas-filled cavity common to all discharge devices is formed between a first and a second block of electrically insulating material. A plurality of transparent anode conductors on a face of a first block of electrically insulating material, sealed to the first block, and in registration with the cavities, form anode electrodes for one co-ordinate of the array. Cathode electrodes are carried by a face of the second block of electrically insulating material, and those cathode electrodes of the other co-ordinate of the array are connected by way of electrically resistive material to one of a plurality of cathode conductors. The cathode conductors, which are isolated from the discharge space or spaces, cathode electrodes and electrically resistive material are all carried on said face of the second block. The first and second blocks may be spaced through a spacer around the edge of the display device or by a third block defining the discharge spaces. A layer of insulating material covers the face of the block, the resistive material and the cathode conductors, except in the vicinity of the cathode electrodes.

21 Claims, 7 Drawing Figures This application is a continuation-in-part of copending application Ser. No. 144,872, filed May 19, 1971 now US. Pat. No. 3,735,183. i This invention relates to visual display devices, and in particular to such devices comprising an array of gasfi lled direct-current cold-cathode discharge devices each of which may be struck or extinguished to produce a display of the required form.

Visual display devices are known which incorporate an array of direct-current discharge devices formed by one or more gas-filled cavities which may be formed in a block of an electrically-insulating material such as glass or ceramic. A set of conductors is formed on a further block which is then sealed to the first block so that the conductors form one electrode of each discharge device. Each discharge device is also provided with a second electrode carried by a face of a third block, also sealed to the first block, and a series impedance connected between that second electrode and one of a second set of conductors.

It has usually been necessary toarrange the series impedances and the second set of conductors outside the display device, though U. S. Pat. No. 3,603,837 describes. and claims a display device with integral lead resistors in which the two sets of conductors may be produced in the same manner.

It is an object of the invention to provide a visual display device of the type described in which the load impedances are formed in a simple manner within the display device.

According to present invention a visual display device incorporating an array of direct current discharge devices comprises one or more gas-filled discharge spacesformed between a firstand a second block of electrically insulating material, a set of electrical conductors on the second block, each conductor forming a first electrode of at least one of said discharge devices, said second block of electrically insulating mate rial being sealed to the first block and a plurality of second electrodes, one for each; of said discharge devices, carried by a face of :the second block adjacent to the discharge space or spaces, at least one set of further electrical conductors formed on said face of the second block and electrically isolated from each discharge space, a layer of electrically resistive material carried by said face of the second block and connecting each second electrode to a selected one of the, or each, set of further conductors and a layer of insulating material covering the resistive material and each further conductor on the surface of the second block. I

The second electrodes, further conductors and electrically' resistive material may all be formed on the surface of the second block and said layer of insulating material extends to said face of said second block between each said electrode and the adjacent one of the, or each, set of further conductors.

The first and second blocks may be spaced by a third block having a plurality of cavities defining said discharge spaces.

The discharge spaces in the third block may comprise a plurality of cavities arranged in a two co-ordinate array and each conductor on the first block may form an electrode for each cavity associated with one coordinate of the array, each one of the, or each, set of further conductors being connected to the second electrodes associated with the cavities of the other coordinates of the array.

The invention will now be described with reference to the accompanying drawings, in which:

FIG. 1 is a sectional side view of a display device according to a first embodiment of the invention;

FIG. 2 is an enlarged view of part of FIG. 1;

FIG. 3 is a sectional side view of a display device according to a second embodiment;

FIGS. 4 and 5 are enlarged views of parts of three further embodiments;

FIG. 6.is a variation of the embodiment shown in FIG. 2 having a layer of insulative material covering the resistive material and each further conductor on the surface of the block; and

FIG. 7 is an enlarged sectional view of a further embodiment.

The display device shown in FIGS. 1 and 2 is made in three parts. The center spacer 10 is a block of glass, preferably a soda-lime glass or similar material, having formed in it a matrix of small cavities 11. These cavities may, for example, be of circular or square crosssection, and are preferably arranged in the rows and columns of a rectangular matrix. The upper block 12, of asimilar material to spacer 10, carries on its underside a number of parallel transparent evaporated anode conductors 13, say of stannic oxide, only one of which is shown in FIG. 1. Each anode conductor 13 passes across the top of all the cavities 11 in one row of the array, which is intended to be viewed from the top as shown in the FIG. 1. 1

The lower block 14, also of a similar material to spacer 10, carries the cathode electrodes 15, load resistors 16 and cathode conductors 17 for the entire matrix of discharge tubes. Each discharge tube has an individual cathode electrode 15 and individual load resistor 16. The cathode conductors 17 comprise a number of parallel strips similar to anode conductors 13,.each strip interconnecting the load resistors 16 associated with a particular column of the matrix. The cathode conductors are spaced from the electrodes of adjacent columns by an air gap or by an insulating material. The complete display device therefore comprises a plurality of discharge cells defined by the cavities 11 in the block 10, the cavities being filled with a suitable gas and closed by the covers 12 and 14. The joints between the various blocks are sealed with a suitable material and provide a gas seal for the device.

The formation of the cathode electrodes 15, load resistors 16 and cathode conductors 17 on the lower cover plate 14 requires a number of operations, and the various components may be made from a number of alternative materials. The load resistors 16 are formed first, by a screen printing process, and are arranged in the appropriate positions on the lower cover plate 14. The resistive material may, for example, be ruthenium dioxide, thallium oxide, irridium oxide or a gold/- platinum mixture in a glass frit. The resistive material must be capable of providing a suitable seriesresistance value of about 1 to 5 Megohm and must be able to withstand a voltage to break down under an operating potential difference of several hundred volts across a length of several thousandth of an inch. The above named materials are capable of producing such resistance values in thick film form. However, they have high melting points and must be bonded to a substrate having a similarly high melting point and a similar coefficient of thermal expansion. The substrate, in this case the block 14, must also have a coefficient of thermal expansion compatible with the soda-lime glass used for the remainder of the construction. A suitable material for the substrate, block 14, is an alumino-soda-lime glass having a melting point of 800 C and a suitable coefficient of thermal expansion. The preferred resistive material is ruthenium dioxide firing at a temperature between 760 C and 860 C and fusing with the glass surface to form a good bond. However, ruthenium dioxide may be fired at about 650 C, while thallium oxide may be fired at about 500 C.

Either the cathode conductors or the electrodes may be formed next. The cathode conductors 17 need not be transparent, and may be formed by evaporating through a mask a layer of chromium with a covering of gold. Finally, the cathode electrodes are formed by a similar process, and may be formed at the same time as the conductors if the same materials are used.

Each cell of the display device may be caused to conduct by applying a DC potential between the anode conductor 13 and cathode conductor 17 which together uniquely define the desired cell. A display may be built up by causing a number of cells to conduct simultaneously.

The resulting display device has the form shown in FIG. 1. However, it is not essential to use a separate spacer block as shown, and this may be replaced by a built-up layer 18 of glass formed by screen printing. The latter arrangement results in a device as shown in FIG. 3, in which the walls l8 defining each individual cell are formed by one or more screen printing operations using a suitable glass. This is used in paste form and subsequently fired. The glass walls 18 cover the load resistors 16 and the cathode conductors 17, leaving exposed only the cathode electrodes 15. The cavities produced have inclined walls due to the build-up of successive layers of the walls 18.

Alternatively, the spacer formation defining individual cells may be omitted altogether, though a spacer is necessary around the edge of the display device. However, if this is done the cathode conductors must be covered. with an insulating material to prevent discharges taking place other than in the required positions.

It has been found in practice that with the arrangement of FIG. 2 when the spacer block 10 is placed adjacentuncovered conductors l7 and resistors 16, that any small air gap between them is liable to result in a discharge being struck between the cell and the conductor l7, by-passing the resistor and burning out the cell with excess current. This is prevented by covering the surface of the block 14, the resistors 16 and the conductors 17 with a layer of insulating material, except in the vicinity of the electrodes 15. Thus, the practical arrangement of FIG. 2 is as shown in the FIG. 6. During fabrication, the resistors 16 and conductors 17 are deposited on the surface of the block 14 and are then covered with a layer of insulating material 19, holes being left in this layer at the positions of the electrodes. The electrodes are then deposited and take on a characteristic dished appearance as part of the electrode extends onto the insulating layer. The spacer block 10 is then placed adjacent the surface of the block 14 as previously.

FIG. 4 also illustrates such an arrangement, where each individual load resistor 16 and the cathode conductors 17 on the block 14 are covered by an insulating layer of glass 19 formed by screen printing and firing a suitable paste. The anode conductors are formed as described previously on the block 13. Only the cathode electrode 15 of each cell on the block 14 is exposed, the insulating layer extending to the surface of the block between each electrode 17 and the adjacent one of the, or each, set of further conductors 17. Thus, the discharges will take place between these electrode and the appropriate row or anode conductors 13.

As before, there is a choice of materials for the conductors, electrodes and resistors, though the materials referred to above are particularly suitable.

Using the constructions referred to above it is possible to provide a matrix of discharge tubes with the individual cells spaced about 0.03 inches apart. This spacing is determined to a certain extent by the resistance of the material used to form the load resistors. If a closer spacing of individual cells is required then a construction such as that shown in FIG. 5 may be used. In this arrangement the cathode electrode and possibly part of the load resistor of one cell overlaps the resistor and cathode conductor of another, being insulated from it by a layer of glass.

As will be seen from FIG. 5 only the cathode conductors 17 are actually formed on the surface of the block 14. The cathode electrodes 15 are formed on top of a layer 19 of insulating glass which covers each cathode conductor and its associated load resistors. It will be seen from a comparison of FIGS. 4 and 5 that the cathode electrodes may be arranged much closer together using the arrangement of FIG. 5 than was possible with the earlier arrangements.

In a. further embodiment, shown in FIG. 7, the lower block 14 carries the cathode electrodes, and a plurality of load resistors and cathode conductors for each discharge cell of the matrix. The resistors are built up in a stack, with insulating material supporting and isolating the various layers. As shown in FIG. 7, three sets of cathode conductors are formed, the three conductors shown being denoted by the references 17a, 17b, and 170, respectively. A first layer 16a of resistive material is formed on the surface of the block 14 with one end of the layer in electrical contact with one of the cathode conductors 17a. Alongside the resistive layer is formed an insulating layer 19a. This insulating layer supports a second layer 16b of resistive material which is connected to a second conductor 17b at one end and which overlaps the first resistive layer 16a at the other end. The remainder of the resistive layer 16a and the conductor 17a are covered by a second layer of insulating material. A third layer of resistive material 16 c is formed over the insulating layer 19b, overlapping layer 16b at one end and making contact with conductor 170 at the other end. The remainder of resistive layer 16b is covered with an insulating layer 190. The center portion of the stack, where the three resistive layers 16a, 16b and overlap, carries the cathode electrode 15 of the cell, the remainder of the stack being covered by an insulating layer 20.

Each cell of the display device thus has one anode connection and three possible cathode connections, any one cell being caused to conduct by applying a suitable DC potential between the anode conductor 13 and a selected one of the cathode conductors 17 which together uniquely define the desired cell.

The intensity of the discharge within the cell depends upon the cathode conductor which is selected. If conductor 170 is used, this is connected through a single resistive layer 16c to the cathode electrode 15, giving a discharge of the maximum intensity. Cathode conductor 17b, however, is connected to the cathode electrode through resistive layer 16b in series with part of layer 160. Hence the total resistance is greater and the discharge current will be lower, giving a discharge of lower intensity. Similarly, the use of cathode conductor 17a causes the total series resistance to be that of layer 16a plus part of each of layers 16b and 16c. This gives the maximum series resistance and hence the lowest intensity discharge. This arrangement may be used with only two, or with more than three, resistive layers and sets of cathode conductors.

Other forms of construction are also possible, so long as theysatisfy the requirement that the load resistors are supported by the surface which carries the associated cathode conductors. For example, a spacer as shown at in FIG. 1 may be used with.constructions of FIGS. 5 and 7, with the spacer separated from the lower cover plate .14 with its resistors and electrodes. The spacer 10 then serves to locate the discharge of each cell in a precise position.

The anode conductors 13 need not be transparent, so long as they are thin enough to avoid seriously obscuring the discharge.

Although in the above embodiments the series resistors have beenconnected to the cathode electrode of each cell, the resistors may alternatively be connected on the anode side of the circuit.

I claim: 1. A visual display device incorporating an array of direct-current discharge devices comprising one ,or

moregas-filled discharge spaces formed between a first and a second block of electrically insulating material, a set of electrical conductors on the face of the first block adjacentthe discharge space or spaces, each conductor forming a first electrode of'atleast one of said discharge devices, means for sealing said second block of electrically insulating material to the first block, a plurality of second electrodes, one for each of said discharge devices, carried by a face of the second block adjacent the discharge space or spaces, at least one set of further electrical conductors on said face of the second block, said further electrical conductors being electrically isolated from each discharge space, a layer of electrically resistive material, carried by said face of the second block and connecting each second electrode to a selected one of the, or each, set of further conductors and a layer of insulating material covering the resistive material and each further conductor on the surface of the second block, the resitance value of the electrically resistive material between each second electrode and a selected one of the, or each set of further conductors being about 1 to 5 Megohm and capable of withstanding a voltage stress of about 10 volts/thousandth of an inch.

2. A visual display device as claimed in claim l in which the electrically resistive material is iridium oxide.

3. A visual display device as claimed in claim 1 in which the electrically resistive material is a gold/- platinum mixture in a glass frit.

4. A visual display device as claimed in claim 1 wherein said second block of material is an aluminosoda-lime glass.

5. A visual display device as claimed in claim 1 in which said electrically resistive material has a melting point of greater than 500 C and said second block of material has a melting point of about 800 C.

6. A visual display device incorporating an array of direct-current discharge devices comprising a first block of electrically insulating material having one or more gas-filled discharge spaces, a second block of electrically insulating material sealed to the first block, a set of electrical conductors on the face of the second block adjacent the space or spaces, each conductor forming a first electrode of at least one of said discharge devices, a third block of electrically insulating material sealed to the first block and a plurality of second electrodes, one for each of said discharge devices, carried by a face of the third block adjacent the discharge'space or spaces, at least one set of further electrical conductors on said face of the third block and electrically isolated from each discharge space, a layer of electrically resistive material, carried by said face of the third block and connecting each second electrode to a selected one of the, or each, set of further conductors and a layer of insulating material covering the face of the block, the resistive material and each further conductor on the surface of the block except in the vicinity of the second electrodes and said electrically resistive material having a resistance value of about 1 to 5 megohm in thick film form and a voltage stress value of about 10 volts/thousandth of an inch.

7. A visual display device as claimed in claim 6 in which eachsecond electrode is stacked over a further conductor associated with an adjacent second electrode.

8. A visual displaydevice as claimed in claim 6 in which the layers of electrically resistive material connecting each second electrode to one further conductor of each 'of a plurality of sets are stacked one above the other and are separated by electrically insulating material.

9. A visual display device as claimed in claim 6 in which the discharge spaces in the first block comprise a plurality of cavities arranged in a two co-ordinate array.

10. A visual display device as claimed in claim 6 in which each conductor on the second block formsan electrode for each cavity associated with one coordinate of the array and each one of the, or each set of, further conductors is connected to the second electrodes associated with the cavities of the other coordinate of the array.

111. A visual display device as claimed in claim 6 in which the first, second and third blocks are of the same electrically insulating material.

12. A visual display device as claimed in claim 6 in which the electrically insulating material .is glass.

13. A visual display device as claimed in claim 6 in which the electrically resistive material is thallium ox ide.

14. A visual display device as claimed in claim 6 in which the electrically resistive material is ruthenium dioxide. 1

15. A visual display device as claimed in claim 6 in which the conductors on the second block are transparent.

16. A visual display device as claimed in claim in which the transparent conductors are of stannic oxide.

17. A visual display device as claimed in claim 6 in which the further conductors are of chromium plated with gold.

18. A visual display device as claimed in claim 6 in which the electrically resistive material is iridium oxide.

19. A visual display device as claimed in claim 6 in material has a melting point of about 800 C.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, I g ug Dated March 1 97 Inventor-(s) Frank Walters It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

[30] I Foreign Application Priority Data "26198/71" should read --26198/70-- Insert:

[73] Assignee z- Ferranti Limited, Hollinwood,

Lancashire, England Signed and sealed this 22nd day of October 1974.-

(SEAL) Attest:

McCOY M. GIBSON JR. c. MARSHALL DANN- Attesting Officer Commissioner of Patents 

1. A visual display device incorporating an array of directcurrent discharge devices comprising one or more gas-filled discharge spaces formed between a first and a second block of electrically insulating material, a set of electrical conductors on the face of the first block adjacent the discharge space or spaces, each conductor forming a first electrode of at least one of said discharge devices, means for sealing said second block of electrically insulating material to the first block, a plurality of second electrodes, one for each of said discharge devices, carried by a face of the second block adjacent the discharge space or spaces, at least one set of further electrical conductors on said face of the second block, said further electrical conductors being electrically isolated from each discharge space, a layer of electrically resistive material, carried by said face of the second block and connecting each second electrode to a selected one of the, or each, set of further conductors and a layer of insulating material covering the resistive material and each further conductor on the surface of the second block, the resitance value of the electrically resistive material between each second electrode and a selected one of the, or each set of further conductors being about 1 to 5 Megohm and capable of withstanding a voltage stress of about 10 volts/thousandth of an inch.
 2. A visual display device as claimed in claim 1 in which the electrically resistive material is iridium oxide.
 3. A visual display device as claimed in claim 1 in which the electrically resistive material is a gold/platinum mixture in a glass frit.
 4. A visual display device as claimed in claim 1 wherein said second block of material is an alumino-soda-lime glass.
 5. A visual display device as claimed in claim 1 in which said electrically resistive material has a melting point of greater than 500* C and said second block of material has a melting point of about 800* C.
 6. A visual display device incorporating an array of direct-current discharge devices comprising a first block of electrically insulating material having one or more gas-filled discharge spaces, a second block of electrically insulating material sealed to the first block, a set of electrical conductors on the face of the seCond block adjacent the space or spaces, each conductor forming a first electrode of at least one of said discharge devices, a third block of electrically insulating material sealed to the first block and a plurality of second electrodes, one for each of said discharge devices, carried by a face of the third block adjacent the discharge space or spaces, at least one set of further electrical conductors on said face of the third block and electrically isolated from each discharge space, a layer of electrically resistive material, carried by said face of the third block and connecting each second electrode to a selected one of the, or each, set of further conductors and a layer of insulating material covering the face of the block, the resistive material and each further conductor on the surface of the block except in the vicinity of the second electrodes and said electrically resistive material having a resistance value of about 1 to 5 megohm in thick film form and a voltage stress value of about 10 volts/thousandth of an inch.
 7. A visual display device as claimed in claim 6 in which each second electrode is stacked over a further conductor associated with an adjacent second electrode.
 8. A visual display device as claimed in claim 6 in which the layers of electrically resistive material connecting each second electrode to one further conductor of each of a plurality of sets are stacked one above the other and are separated by electrically insulating material.
 9. A visual display device as claimed in claim 6 in which the discharge spaces in the first block comprise a plurality of cavities arranged in a two co-ordinate array.
 10. A visual display device as claimed in claim 6 in which each conductor on the second block forms an electrode for each cavity associated with one co-ordinate of the array and each one of the, or each set of, further conductors is connected to the second electrodes associated with the cavities of the other co-ordinate of the array.
 11. A visual display device as claimed in claim 6 in which the first, second and third blocks are of the same electrically insulating material.
 12. A visual display device as claimed in claim 6 in which the electrically insulating material is glass.
 13. A visual display device as claimed in claim 6 in which the electrically resistive material is thallium oxide.
 14. A visual display device as claimed in claim 6 in which the electrically resistive material is ruthenium dioxide.
 15. A visual display device as claimed in claim 6 in which the conductors on the second block are transparent.
 16. A visual display device as claimed in claim 15 in which the transparent conductors are of stannic oxide.
 17. A visual display device as claimed in claim 6 in which the further conductors are of chromium plated with gold.
 18. A visual display device as claimed in claim 6 in which the electrically resistive material is iridium oxide.
 19. A visual display device as claimed in claim 6 in which the electrically resistive material is a gold/platinum mixture in a glass frit.
 20. A visual display device as claimed in claim 6 wherein said second block of material is an alumino-soda-lime glass.
 21. A visual display device as claimed in claim 6 in which said electrically resistive material has a melting point of greater than 500* C and said second block of material has a melting point of about 800* C. 